The present invention relates to liquid inks. More particularly, it relates to liquid inks for marking instruments.
Marking instruments, e.g., pens and markers, have a tip to which a liquid ink is supplied from a reservoir to be applied onto a substrate, such as a sheet of paper, by means of the tip which is moved over the surface of the substrate to leave a liquid trace.
Traditionally, liquid inks for marking instruments either have a viscosity of about 5 centipoise (xe2x80x9ccpsxe2x80x9d) or lower (e.g., for fiber tip pens or fountain pens), or have a viscosity of about 7,500 cps or higher (e.g., for ball point pens). The latter usually contain a certain amount of a polymeric material(s).
One of the features of the present invention involves non-erasable liquid inks for marking instruments with a distinctive range of viscosity.
Thus, one aspect of the invention relates to a non-erasable liquid ink, with a water content of about 0-15% by weight, for a marking instrument. By xe2x80x9cerasable inkxe2x80x9d is meant an ink, which, after being deposited on a porous substrate, cannot be erased using a conventional rubbery eraser. The non-erasable ink includes a solvent and a colorant, e.g., a dye or a pigment, dissolved or dispersed in the solvent, and has a viscosity of about 15 to 4,500 cps. More preferred ranges of viscosity include, but are not limited to, about 50 to 2,000 cps, about 100 to 1,000 cps, or about 150 to 600 cps. The viscosity of an ink of this invention described herein is that measured at a shear rate of 300 secxe2x88x921 at room temperature.
The liquid ink may also contain one or more polymers with averaged molecular weights ranging from about 1xc3x97104 to 1xc3x97106 daltons (preferably, about 1xc3x97105 to 6xc3x97105 daltons) with the total content of the polymer(s) being about 0.05% to 2.5% by weight of the ink. A more preferred range of the total polymer contents is about 0.05% to 1.0%. It is particularly preferred that the total polymer content be about 0.3%. Examples of suitable polymers include, but are not limited to, polyvinylpyrolidone (xe2x80x9cPVPxe2x80x9d) and, ketone/formaldehyde resin.
Preferably, one or more lubricants, such as oleic acid or oleic diethanolamine (xe2x80x9cODEAxe2x80x9d), can be incorporated in the liquid ink as to decrease friction resulting either from contact between a marking instrument and the substrate (e.g., paper) onto which a marking is being made, or, in the case of a ballpoint pen, from contact between the roller ball and the socket, thereby enhancing smoothness in using the marking instrument.
The colorant used in the liquid ink may be either a dye (i.e., which can be dissolved in a solvent), or a pigment (i.e., which can only be dispersed, rather than dissolved, in a solvent). When a pigment is used, it is preferred that a gelling agent be also included in the ink so as to prevent pigment sedimentation or ink leakage.
Another aspect of this invention relates to a non-erasable liquid ink, with a water content of about 0-15% by weight, for a marking instrument which includes (i) one or more polymers with averaged molecular weights ranging from about 1xc3x97104 to 1xc3x97106 daltons, preferably, about 1xc3x97105 to 6xc3x97105 (e.g., PVP or ketone/formaldehyde resin), (ii) a colorant, and (iii) a solvent, with the total content of the polymer(s) being about 0.05% to 2.5% by weight (more preferably, about 0.05% to 1% by weight) of the ink. In a particularly preferred embodiment, the total polymer content is about 0.3% by weight. Similarly, whenever necessary, other ingredients, such as a lubricant or a gelling agent, can also be included in the ink.
Note that a colorant incorporated in an ink of this invention does not include a colored polymer, e.g., polymeric dyestuff. Similarly, a polymer used in this invention is, by definition, not colored. By xe2x80x9cpolymerxe2x80x9d is meant a macromolecule consisting essentially of repeating units with a molecular weight of at least 1xc3x97104 daltons. A preferred M.W. range is about 1xc3x97104 to 1xc3x97106 daltons. A particularly preferred M.W. range is about 1xc3x97105 to 6xc3x97105 daltons.
Also within the scope of this invention is a marking instrument which includes: a body, a reservoir chamber within the body, and a liquid ink in the chamber. The liquid ink may be an ink of the present invention as described above, or an ink of a lower viscosity which is most suitable for use in fiber tip pens or fiber tip highlighters.
Preferably, the marking instrument further includes an ink feed device having a channel for conducting the ink from the chamber to a marking tip, an elastomeric member which partly confines the chamber and supports the feed device with respect to the body, and a valve defined by the feed device and the elastomeric member for controlling communication between the chamber and the channel, whereby the feed device is retractable relative to the body under a force exerted against the tip, and in response to such retraction the chamber is pressurized by deflection of the elastomeric member and the valve is opened to allow the ink to enter the channel from the chamber. Note that the marking instrument constructed in a manner described above may be equipped with a variety of different marking tips (e.g., a roller ball) and is not limited to any particular type of tip.
A further aspect of the present invention relates to a method of making a marking on a substrate, e.g., a piece of paper. The method includes the steps of: providing one of the above-described liquid inks of this invention, and applying the liquid ink against a surface of the substrate forming a marking.
One feature of the invention is the use of the valved ink feed device which allows lower viscosity ink to flow to the marking tip only when the tip is pressed against a writing surface. Without this valve restricting flow to the tip, the lower viscosity ink would tend to leak from the marking tip. By use of this valved ink feed device, lower viscosity ink can now be used, the ink having lower writing friction when applied.